Azoxystrobin is a novel, high-efficient, broad-spectrum, systemic fungicide that can be used for spraying on stems and leaves, and seed processing as well as soil processing. However, there exist some problems in the synthesis of azoxystrobin including, for example, the impossibility of catalyst recycling, the high costs, the difficulties in post-processing and the low yields, which affect the application of azoxystrobin.
CN101163682 discloses a method for preparing azoxystrobin by reacting 2-cyanophenol with a compound represented by formula (I) under the catalysis of DABCO. The amount of DABCO used in this method is 0.1-2% in mole relative to the compound represented by formula (I) and the compound represented by formula (I) has a structure of
wherein w is methyl (E)-2-(3-methoxy) acrylate group, i.e. C(CO2CH3)═CHOCH3, or methyl 2-(3,3-dimethoxy) propionate group, i.e. C(CO2CH3)CH(OCH3)2, or a mixture of the two groups. In this method, the reaction yield can reach 98.7% with the catalyst DABCO in a polar aprotic solvent DMF having a high boiling point (150° C.). During post-processing, the DMF is firstly removed by vacuum distillation and then toluene and water are added and stirred until stratification, to provide a toluene solution containing azoxystrobin. Most of the catalyst comes into wastewater due to the good water solubility of DABCO and the catalyst DABCO cannot be recycled due to its high boiling point (174° C.), resulting in increased costs and high total nitrogen and COD in wastewater, which are difficult to process. During the post-processing of this method, there is a need for high vacuum distillation (to remove DMF at 100° C.), which increases the difficulties in workshop operation, as well as a need for subsequent addition of toluene and water, which causes a cumbersome operation.
In addition, EP0794177 discloses a method for synthesizing an asymmetric 4,6-disubstituted pyrimidine by reacting a substituted chloropyrimidine compound with trimethylamine to form a substituted pyrimidine halogenated quaternary ammonium salt, in which the amount of trimethylamine is 3 times more than that of the substituted chloropyrimidine. The substituted pyrimidine halogenated quaternary ammonium salt is separated and subjected to a reaction with a phenolic compound in an organic solvent to prepare an asymmetric, 4,6-disubstituted pyrimidine compound. The amount of trimethylamine used in this method is large; and the obtained quaternary ammonium salt needs to be separated, and the separation yield is low, only about 80%; in addition, two steps are needed to obtain 4,6-disubstituted pyrimidine compound, which causes a cumbersome industrial operation.
Therefore, such a method for preparing azoxystrobin is desired in the art that in this method the catalyst can be recycled, the total nitrogen and COD in wastewater are reduced and a “one-pot synthesis” can be achieved, and the method is convenient for industrial operation, has the advantages of environmental protection and high yield.